fix core build
fix core build

bin/buildout -c buildout-core.cfg failed with the following error:

While:
  Installing.
  Getting section frontend_development.ini.
  Initializing section frontend_development.ini.
Error: Referenced option does not exist: adhocracy redirect_url

liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator